196 C. M. CHILD 



Thus far comparison of the rate of C02-production has been 

 made between relatively long anterior and posterior pieces, 

 between short anterior and posterior pieces, between animals in 

 different nutritive condition, between early and later stages of 

 regulation and between mo\'ing and quiescent animals and in 

 every case the result obtained paralleled that obtained by the 

 direct method. Moreover, in almost every case the result was 

 obtained without knowledge of the result which I had obtained 

 with the resistance method. I am under great obligation to Dr. 

 Tashiro, both for his kindness in making the tests and for permis- 

 sion to make this statement. 



These data obtained by a totally different method from my 

 own afford a most valuable confirmation of the results of the resist- 

 ance method. The only possible conclusion is then, I believe, 

 that the resistance of Planaria — as well as of various other forms 

 — to certain reagents is in general a measure of the rate of meta- 

 bolic reaction and can be used as a basis for comparing the rates 

 of reaction of different animals and pieces under different internal 

 and external conditions. 



6. The value and the limitations of the resistance method 



It is evident that so long as disintegration is the criterion of 

 death, this method can be used only in cases where death is fol- 

 lowed within a short time by disintegration. So far as my experi- 

 ence goes, this occurs only in those forms where a highly differ- 

 entiated connective tissue or a well developed skeleton is absent. 

 For example, the method gives very definite results in the earlier 

 stages of amphibian ontogeny, but by the time the animals 

 hatch, the skeleton and connective tissue have attained a con- 

 sistency such that disintegration does not occur for days after 

 death. If we can find some other satisfactory criterion of death, 

 we can of course apply the method much more widely. Failing 

 this, it may be possible to use the indirect method to some extent 

 in such cases, for with that method determination within a day or 

 two of the time of death is in most cases sufficient. As yet I have 

 not attempted to develop the method along this line. 



